My long-term career goal is to investigate viral- and host-specific mechanisms that contribute to the pathogenesis of respiratory viral infections, in order to develop novel therapeutic intervention, as well as viable vaccine candidates. The K22 award will help me by providing the initial support necessary to establish a career as an independent investigator. Human metapneumovirus (hMPV) is a recently identified respiratory virus belonging to the Paramyxoviridae family. It is a leading cause of respiratory infections in children. Little information is available regarding the pathogenesis of hMPV infection. The aim of this proposal is to investigate host cellular responses to hMPV infection using a combination of molecular virology, cellular biology and protein chemistry techniques. I have recently shown that the RNA helicases-MAVS signaling pathway plays a significant role in hMPV-induced expression of immune and inflammatory genes, including type I interferon and chemokines, which are regulated through the activation of Nuclear Factor-? B (NF-?B) and Interferon Regulatory Factors (IRF) transcription factors. Preliminary studies demonstrated that hMPV glycoprotein G and small hydrophobic protein SH modulate hMPV-induced cellular responses by likely disrupting RIG-I- and PKA-dependent signaling. The goal of this proposal is to identify molecular interaction between host signaling molecules and viral proteins and will be accomplished through the following specific aims: Aim 1. To define the molecular mechanism whereby G inhibits RIG-l-mediated signaling. In this aim, we will investigate whether G protein expression interferes with RIG-I dependent signaling by disrupting the association of RIG-I with its downstream adaptor MAVS and/or by sequestering viral RNA from RIG-I. We will also identify which residues of G are important for modulating hMPV-induced cellular signaling. Aim 2. To define the molecular mechanism whereby SH inhibits NF-?B activation. In this aim, we will first determine the mechanism by which SH inhibits NF-?B phosphorylation. We will then map SH residue(s) critical for its inhibitory activity. RELEVANCE (See instructions): Upon completion of the proposed studies, we will obtain new critical information on the mechanisms of hMPV-induced cellular signaling, which may allow us to specifically modulate viral-induced gene expression and therefore antiviral and innate immune/inflammatory responses. The results obtained from these studies will be instrumental for the development of future hMPV vaccine candidates which are safe and effective.